1. Field of the Invention
The present invention relates to a battery pack apparatus with a plurality of medium feeding parts for adjusting a temperature thereof. In particular, the present invention relates to a battery pack apparatus preventing all of the medium feeding parts from rotating at almost the same revolution.
2. Description of the Related Art
In recent years, in a battery pack apparatus with the battery assembly having a configuration in which a plurality of secondary batteries is connected in series, a calorific value on electric charging or discharging becomes larger as secondary batteries have a larger capacity and supply a larger current. For that reason, it is necessary to enhance a cooling capacity of an apparatus for cooling down the battery assembly in battery pack apparatus. In battery pack apparatus, when the cooling apparatus detects an increase of a temperature of the battery assembly by, for example, temperature-detecting elements or the like, the cooling apparatus makes fans or the like rotate to feed cooling air to the battery assembly and a neighborhood thereof to cool down at least a part of the battery assembly. In the case of the battery assembly with a high calorific value, a plurality of fans is provided for a single battery assembly. In the case of the battery pack apparatus having a plurality of battery assemblies, one or more fans are allocated for each battery assembly.
In the above-mentioned battery pack apparatus with a plurality of fans, peak frequencies of noises generated by the respective fans rotating at almost the same revolution are overlapped each other, which causes a large noise. According to a method for cooling an equipment of a prior art disclosed in the Japanese patent laid-open publication No. 2005-130531, two or more fans, all of which are the same type, are controlled at different revolutions from each other. This leads that the peak frequencies of noises generated by the respective fans are shifted to each other to be different from each other, and resulting in reduction in the noise.
However, in the cooling method of the prior art, there is a difference in cooling capacities of the fans controlled at different revolutions from each other, which feed cooling medium such as cooling air or cooling gas or the like. As a result, there is such a problem that the battery assembly, which is a cooling object, is not uniformly cooled down. In addition, there is another problem that the noise and the vibration are increased when a composite oscillation waveform generated by a plurality of fans rotating at different revolutions from each other corresponds to a resonance point oscillation waveform of a package, which packs the battery pack apparatus therein.